Also a broken thermostat that's open (or if the thermostat is missing) will allow for too high of a fluid flow through the block limiting how much heat the coolant can absorb and transfer to the radiator.

Hope it helps, good luck!

Was wondering why my car was running hot (right around red zone). Removed a failed thermostat on a trip into NYC, figured it'd just run colder without it. Was actually starting to think it might have been a failing water pump.